Recently we got the great news that we were awarded funding from NASA’s Office of Chief Technologist for the NASA Innovative Advanced Concept (NIAC) proposal “Super Ball Bot – Structures for Planetary Landing and Exploration.” The proposed research revolves around a radical departure from traditional rigid robotics to “tensegrity” robots composed entirely of interlocking rods and cables. Out of more than 600 white papers originally submitted, this proposal is one out of only 18 that were funded for 2012. Tensegrities, which Buckminster Fuller helped discover, are counter-intuitive tension structures with no rigid connections and are uniquely robust, light-weight, and deployable. Co-led by Vytas SunSpiral (Intelligent Robotics Group) and Adrian Agogino (Robust Software Engineering Group), and collaborating with David Atkinson of the University of Idaho, the project is developing a mission concept where a “Super Ball Bot” bounces to a landing on a planet, then deforms itself to roll to locations of scientific interest. This combination of functions is possible because of the unique structural qualities of tensegrities which can be deployed from small volumes, are lightweight, and can absorb significant impact shocks. Thus, they can be used much like an airbag for landing on a planetary surface, and then deformed in a controlled manner to roll the spacecraft around the surface to locations of scientific interest.

A concept drawing of the mission, where many Super Ball Bots could be deployed and bounce to a landing before moving and exploring the surface.

These unusual structures are hard to control traditionally so Vytas and Adrian are experimenting with controlling them using machine learning algorithms and neuroscience inspired oscillatory controls known as Central Pattern Generators (CPG’s). Adrian’s work on multiagent systems and learning provide robust solutions to numerous complex design and control problems. These learning systems can be adaptive, and can generate control solutions to complex structures too complicated to be designed by hand. This approach is well suited for tensegrity structures which are complex non-linear systems whose control-theory is still being developed. Vytas has been researching robotic manipulation and mobility for over a decade and in recent years has been focused on the game-changing capabilities of tensegrity robots due to their unique structural properties. His quest to tap their potential has lead him to investigate oscillatory control approaches from the field of neuroscience, such as Central Pattern Generators (CPG’s), which show promise for efficient control of these robots.

A concept drawing of the Super Ball Bot structure

While the Super Ball Bot project has just started, we already have some exciting initial results from the machine learning efforts. During the last year, Vytas led the development of a physics based tensegrity simulator built on-top of the open-source Bullet Physics Engine. We have been using that simulator to explore novel tensegrity structures and control approaches, and will write a separate post about the oscillatory control of a snake-like tensegrity robot and its ability to traverse many complex terrains with fully distributed control algorithms. The following video shows two drop tests where we simulate a tensegrity robot landing. The results confirm what we see in physical models in our lab, which is that these structures do a great job absorbing impact forces, even as we vary the stiffness of the strings.

Since the NIAC proposal was awarded, we have focused on evolving the motion controls of a rolling tensegrity robot and have early simulation results which show it safely rolling through a rocky terrain.

To date, most of the research into control of tensegrity robots has focused on slow motions which do not excite the dynamics of the structure. Wanting to show that tensegrity robots can be fast and dynamic movers, we are exploring what is possible when the structure is driven at the limits of dynamic stability.

To explore the maximum speed achievable by our tensegrity robot, Adrian’s intern, Atil Iscen, has been developing an evolutionary control approach where a large population of random tensegrity controllers are evaluated based on their ability to move the farthest distance within a fixed amount of time. Then, the worst performing members are eliminated from the population and the best ones are replicated and mutated, allowing the mutations of the good controllers to become even better.

Our best solutions so far evolve parameters to a distributed oscillatory controller where the lengths of groups of three cables (making a facet) are controlled by the values of a sine-wave. The job of evolution is then to control the phase offset, period, and amplitude of the sine wave for the strings. The breakthrough of this approach is that it enables fast dynamic motion, without requiring the computationally expensive modeling and analysis necessary for a centrally computed controller.

Our preliminary results show that tensegrity robots are indeed capable of fast dynamic motion, and that the evolutionary approach is successful at finding difficult to model dynamic controllers.

In the following video we show:
1) Slowly moving hand-crafted controller showing the difficulty of this problem.
2) An evolved controller showing high speed mobility
3) An evolved controller showing high speeds while handling rough terrain

While it is exciting to see such fast and dynamic motion from a tensegrity robot, rolling at the limits of stability is not the control approach we need for a space mission. When exploring another planet we need to balance the needs of making progress with concerns about energy efficiency and stability. Thus, we evolved a new controller with a tighter cap on the amount of stretch and energy available for each string. With that change we find results which appear stable and far more appropriate for exploration of a distant planet.

These results are preliminary and we expect to continue to improve the stability, energy efficiency, and terrain handling. Still, it is important to explore the upper limits of speed and dynamic performance. Further, we are establishing that evolutionary approaches are capable of parameter tuning and optimizing the performance of distributed control systems for dynamic tensegrity robots. This is important due to the deep challenges in hand crafting the dynamics of these complex and non-linear systems.

Moving forward we plan on exploring increasingly complex structures and distributed control architectures within which we will deploy our learning algorithms to tune performance. In other work we have already shown success at deploying distributed impedance control on tensegrity robots, along with compelling results from biologically inspired Central Pattern Generators (CPG’s). Both of these approaches require significant amounts of hand tuning of parameters, which our learning algorithms should be able to improve upon. Beyond the evolutionary approaches used so far, we also expect to explore multiagent control.

3 Responses

Have the possibilities of making such a device amphibious been considered? because it appears to me that this form of motion would not only be capable with some minor adaptations of your rod design (move from a cylindrical shaft to more of a wing or paddle shape) but quite possibly highly adept.
This being said once the initial designs are proven this design looks to me to be perfect prospect for miniaturisation, maybe one day you will have nano-sized structures very similar to this flowing through your blood stream.

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About BeingHuman

Greetings!
Here you will find my thoughts on being human, based on my ongoing research into robotic and human motion, neuroscience, physiology, and machine learning. You will also find videos of my talks and papers from the Dynamic Tensegrity Robotics Lab which I lead at the NASA Ames Research Center.

Archive of all past posts

Archive of all past posts

My Favorite Ergonomic Equipment

Based on my understanding of human physiology and motion, here are some quick reviews on my favorite ergonomic tools. These are the ones I use at home and at work. I will add more in-depth posts discussing the alignment theory as I get them written.

FitBall Sitting Disc
Sitting Discs are a great way to train for Active Sitting. By destabilizing the surface you are sitting on, they engage your core muscles and keep you in dynamic motion while your body actively balances on the disk. I recommend the larger 15" disc. In Depth Review

Salli Saddle Stool
The Salli saddle stools are one of the best stools for Active Sitting. They hold your pelvis upright, so that your spine can be well aligned with gravity, while also allowing your knees to be lower than your hips to keep your hamstrings and hip-flexors from shortening. Actively sitting takes effort, so increase your time in the saddle slowly.

3M Ergonomic Mouse
The vertical design keeps the arm in a well aligned neutral "handshake" position that prevents the shoulder from rolling forward. By keeping your shoulders back and the scapula flat on your back you avoid many of the common sources of wrist pain. This is the biggest bang for your buck if you are having wrist pain. It comes in small and large sizes (small is linked below). Sadly, I have only seen it for right hands.

ErgoMagic Keyboard
Like the 3M mouse above, this keyboard allows you to have your hands in a more neutral vertical position which reduces many of the problems associated with wrist and shoulder pain. It also allows you to spread the key pads to be at shoulder width so that you don't have to twist your wrist like on a straight keyboard.

Sit-Stand Desk
A sit stand desks allows you to dance while working! It also allows you change between a variety of different sitting options and standing so that you don't get stuck in one position. The best option that I have found is from GeekDesk.com. I have two from them and they are the cheapest and have held up well. You can save even more money by buying just the base frame from GeekDesk and getting the table top from Ikea. You save on price and shipping is significantly less this way.

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Books I Recommend

Sync: How Order Emerges From Chaos In the Universe, Nature, and Daily Life
This book blew my mind.
Really -- this was probably one of the most influential books I've read in a decade. This points straight at the heart of what we intuitively recognize as the difference between living breathing organic aspects of nature and the mechanistic nature of human engineered system. It all boils down to oscillators and their ability to synchronize. This basic mathematical property is the basis for all the order that we see in the world -- and our ability to move -- and our ability to relate to each other -- and really everything. This is an easy and engaging read, and you will come away with new eyes for the world.

Anatomy of Movement
This was the best book I have read for learning about the function of my own body and is endlessly useful for anyone who is alive and moving in the world. Ever have pain when you make a specific motion and wonder what is going on? This book will help you isolate the muscles responsible for that motion. By showing how each muscle moves your body under different conditions, you will learn their *use* rather than just memorizing a bunch of names.

Anatomy Trains: Myofascial Meridians for Manual and Movement Therapists
This book is great to see and understand the complex network of tension in the living body, and to learn about fascia and how it works.

Rhythms of the Brain
This recently published book covers cutting edge theories of how the brain works. The key focus is on how the brain relies heavily on coupled oscillatory networks, timing loops, and synchronization. It also discusses how the activity in the brain can be viewed as a dynamic tensegrity structure. A more technical book, but well worth the effort!